Can anyone tell me why the icing isn't producing an "ooze" effect?
I had this problem too.

You have enabled the snapping option. Change the offset in your Solidify Modifier (1 or -1) of the icing part.

Remember, when you grab that point, you will pull the part and at a certain point, the vertices that are at the top that point will intersect with the donut. You can prevent that by adding or subdivide your face. With that, you will have more points to control for the ooze effect